Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

607
FXUS63 KLOT 180600
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
100 AM CDT Mon May 18 2026

.KEY MESSAGES...

- Additional rounds of showers and thunderstorms Monday through
  Tuesday, some of which could be severe at times.

- Summer-like warmth and breezy winds at times will prevail
  through Tuesday before cooler temperatures return for the
  middle of the week.

&&

.DISCUSSION...
Issued at 130 PM CDT Sun May 17 2026

A robust convectively-augmented MCV continues to pivot north out
of southern Wisconsin and away from our region early this
afternoon. Modest large scale height rises will develop over the
local region which will promote precip-free conditions across
the area the rest of the afternoon. The one exception might be
across our far northwest where some lingering glancing ascent
co-located with cooler mid-level temperatures may support some
lingering spotty sprinkles.

In advance of our next weather-maker, tonight will feature warm
and somewhat humid conditions. With a tightening surface
pressure gradient and only modest decoupling, should see at
least intermittent gusty southerly breezes through the night.

Expansive strong to severe convection is expected to develop
later this afternoon and evening across the central and
northern Great Plains along an eastward-advancing cold front.
Given the strong nature of low-level forcing with the front,
it`s not surprising that there`s good model agreement suggesting
upscale growth into one or two expansive MCSs through the
evening hours. While some timing discrepancies remain, there`s a
general consensus for this activity to approach our forecast
area just prior to daybreak Monday morning. Deep layer shear
over the local area is not forecast to be particularly robust,
and generally oriented from southwest to northeast, roughly
parallel to the progged MCS(s). This overall is not favorable--
combined with the time of day and nocturnally-stabilized
boundary layer--for robust convective sustenance.

At this time, it appears the most probable scenario is for a
decaying thunderstorm complex, potentially with lingering strong
gusty outflow and maybe some cores with a small hail potential,
to push into the region through Monday morning. In this
scenario, expansive cloud cover, trailing stratiform rain, and
some embedded thunderstorms may linger well into Monday
afternoon across the northwest half of the CWA (roughly NW of
I-55). This would obviously significantly reduce the subsequent
afternoon severe weather threat across this area.

If this morning complex doesn`t just surge through the entire
forecast region (which remains a potential), muted insolation,
with the bulk of the anvil blow off likely streaming northeast
as opposed to easterly, may facilitate destabilization through
midday and into the afternoon south and east of I-55. This could
support gradually-increasing storm organization and
intensification. That said, progged shear profiles still aren`t
anything spectacular with the main mid/upper jet cores still
relegated well to the west. Given this, it seems like the
locally greatest threat for strong-severe storms exists across
the eastern half of the CWA from about midday through the
afternoon. In this scenario, deeper boundary layer mixing would
also promote increasing southwesterly wind gusts, possibly
pushing 40 mph. If the overnight complex fizzles prior to
reaching our area, the severe threat would likely increase
across more of the region, although this currently looks like a
lower potential at this time based on the latest multi-model
consensus.

Today`s guidance paints a similar picture/evolution to things
for Monday night into Tuesday as the main cold front will sweep
west to east through the region Tuesday afternoon. Once again,
a potential for mainly sub-severe morning convection exists,
followed by a threat for more robust storm development on the
advancing cold front midday into the afternoon. While deep layer
shear is forecast to be a bit more significant than Monday,
instability could once again be muted significantly by morning
convection.

In the wake of the cold front, breezy northwesterly winds will
develop Tuesday/Tuesday night before turning north/northeasterly
on Wednesday as high pressure builds into the region. A period
of tranquil weather is in store until the end of the week and
next weekend when the next series of disturbances will bring
additional chances of showers and perhaps some thunderstorms to
the area.

Carlaw

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 100 AM CDT Mon May 18 2026

Forecast concerns for the terminals...

- Line of showers and embedded thunderstorms to move through
  northern IL and northwest IN late tonight into Monday morning.
  A few storms could be strong with a threat for locally gusty
  winds.

- Breezy south-southwest winds Monday afternoon with gusts
  around 25 kts.

- Another period of showers and possible storms late Monday
  night into Tuesday morning.


Latest radar imagery continues to show a line of showers and
thunderstorms stretching from MN to KS that is racing towards
northern IL and eventually northwest IN. Arrival time of this
line continue to be around 09z at RFD and between 10-12z for the
Chicago area terminals. While lightning trends within the line
segment heading towards the terminals has been decreasing,
recent AMDAR sounding out of MDW continue to show steep mid-
level lapse rates (around 7-8 C/km) which could still support an
occasional lightning strike as the line moves through.
Additionally, a few stronger showers/storms are possible and
could result in localized gusty winds and maybe some small hail.

Once the line of showers/storms arrives, it should move through
within 3-4 hours at each site. However, with the expected
arrival time around daybreak there continues to be a chance that
some renewed development could occur within the line as it
traverses the area, especially south of I-80. If this occurs as
guidance suggests then shower/storm activity could persist
through the morning before things fully exit the area. It was
for this reason that the long PROB30 was maintained, but
hopefully we can refine this window as the line arrives.

After the line exits the area around midday, breezy south-
southwest winds will develop and persist through the afternoon.
Gusts during this period look to generally be around 25 kts but
locally higher gusts (upwards of 30kts) are possible. While
there is still a non-zero chance (15-20%) for additional shower
and/or thunderstorms to develop this afternoon, latest guidance
trends have continued to back off on this scenario given that
the better forcing for storms will be centered to our west in
IA. That said, another round of showers and thunderstorms is
expected to develop in IA this afternoon and move into northern
IL and northwest IN late Monday night into Tuesday morning.
Though, the coverage of these storms into our area looks much
more limited (especially the thunder coverage) so have opted to
introduce a PROB30 for SHRA in the 30-hour TAFs for now.

Otherwise, expect VFR conditions to prevail through the period.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 AM CDT early this morning for the
     IL and IN nearshore waters.

&&

$$

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